Assessing the impact of coal mining activities on soils and terrestrial organisms using land snail Achatina fulica as a bioindicator
Loading...
Date
2022
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
A lack of evaluation of soil quality in Zimbabwe's coal mining regions threatens the soil's
ability to support biological productivity. Reports from the Environmental Management
Agency of Zimbabwe and the Centre for Natural Resources Governance showed that the river
(Deka) that flows through the study area was polluted. Pollutants in the Deka River were
possibly emanating from land, but there was no scientific evidence. Hence it was important to
evaluate pollution on land in the coal mining area. The biochemical response of the land snail
Achatina fulica, exposed to soils collected from the coal mining area, was used to assess soil
health. The level of selected heavy metals and polyaromatic hydrocarbon (PAH) levels were
determined in soil samples obtained from 7 different sites at a coal mining area over a 2-year
period (2018 to 2019). Soils obtained from the coal mining area were used to expose land
snails acquired from a comparatively pure environment and acclimated to laboratory settings
(for 1 year). The coal mining region's soils were determined to be mildly acidic (pH 5.53).
Solubility of some metal elements increases when soils are acidic thus making such metals
bioavailable and possibly increasing metal toxicity. The concentrations of heavy metals in
soil samples from the coal mining area were significantly higher than in control soils (p <
0.05). The concentrations of zinc and cadmium were found to be above the World Health
Organisation maximum permissible limits of 50 and 0.8 mg/kg respectively in the study
period. Zinc and cadmium had mean concentrations of 164.40±81.82 and 0.97±0.27 mg/kg
respectively. Results of regression analysis indicated that cadmium, lead and zinc were highly
bioaccumulated with regression coefficients of 0.90, 0.94 and 0.95 respectively.
Metallothionein induction in snail tissue often happen upon exposure of snails to certain
metals such as cadmium. The highest levels of metallothioneins were observed in snail tissue
exposed to soils with the highest concentration of heavy metal levels. The concentrations of
naphthalene, acenaphthene, phenanthrene, anthracene, flouranthene, pyrene,
benzo(k)fluoranthene, benzo(a)pyrene and indeno(1,2,3-c,d)pyrene in soils from the thermal
power plant area were higher compared to soil from the control site (p < 0.05). High
molecular weight (HMW) polycyclic aromatic hydrocarbons were predominant in soil
samples from the coal mining area compared to low molecular weight polyaromatic
hydrocarbons. High molecular weight polyaromatic hydrocarbons are carcinogenic and
benzo(a)pyrene is the most potent. The thermal power plant area had the highest proportion
of HMW polyaromatic hydrocarbons thus organisms around the area were likely to be at high
risk of cancer and mutations. The sum of 14 polyaromatic hydrocarbons (Σ14 PAHs) at all
sites was significantly higher than the 1000 µg/kg allowable in soil by United States
Environmental Protection Agency. The ratio of anthracene to the sum of anthracene and
phenanthrene was above 1 in soils from the disused coal processing area (Site C), active coal
processing area (Site E) and thermal power plant area (Site F). This indicated that
polyaromatic hydrocarbons in soils from Site C, E and F mostly emanated from wood, grass
and coal combustion. There was a general increase in heavy metal and PAH levels from 2018
to 2019. This was probably because the study area is semi-arid hence leaching and runoff was
minimal in soils from the coal mining area. Antioxidant enzyme (superoxide dismutase,
catalase, glutathione peroxidase and NAD(P)H quinone reductase) and xenobiotic
metabolising enzyme (glutathione S-transferase and ethoxyresorufin O-deethylase) activities
were significantly increased in snails exposed to soils from the coal mining area compared to
the control soil (p < 0.05). The high antioxidant enzyme activities showed that the snails were
adapting to the effects of reactive oxygen species or experiencing oxidative stress. The
highest xenobiotic metabolising enzyme activities were observed in snails exposed to soil
from the coal tailing and power plant area. Persistent exposure (45 days) of land snails to
contaminated soils markedly increased biomarker responses in land snails. Results showed
ii that land snails are sensitive bioindicators and may be used to monitor pollution on land.
Further more, results showed that combining biomarker measurements and chemical analysis
can be a useful approach in evaluating the health of invertebrates in terrestrial ecosystems and
the soil quality. The data obtained in this study can be included in soil ecotoxicological data
and used in formulating soil quality management frameworks of the area.
Description
Keywords
Citation
Ndebele D. (2022) Assessing the impact of coal mining activities on soils and terrestrial organisms using land snail Achatina fulica as a bioindicator [M.Phl. thesis]. - Bulawayo: National University of Science and Technology]